Mosquitoes carrying West Nile virus have been found in Gardena, Carson, Harbor City, Wilmington and San Pedro, all within miles of Manhattan Beach, Hermosa Beach and Redondo Beach.
The California Department of Public Health reported 126 human West Nile cases statewide as of Sept. 11, up from 31 at the same point in 2025. Nine infections were fatal. LA County alone accounted for 43 cases, and 26 new cases were reported countywide in a single week.
The virus got a head start this year. Susanne Kluh, general manager of the Greater Los Angeles County Vector Control District, said in August that West Nile activity in LA County began almost two months earlier than usual after the warmest winter on record, as reported by the Los Angeles Times.
Of the 126 statewide cases, 84% involved neuroinvasive disease, which can cause meningitis, encephalitis and paralysis. The median age of patients was 64. No vaccine or specific treatment exists for West Nile. About one in five infected people develop fever and other symptoms, and about one in 150 develop severe illness, according to ABC7 citing health officials.
Statewide, 3,424 mosquito pools have tested positive for West Nile in 2026, compared with 2,097 at the same point last year. About 24% of dead birds collected through surveillance carried the virus, nearly double the five-year average of 13%.
West Nile is not the only mosquito-borne threat gaining ground. California has confirmed nearly 20 cases of locally transmitted dengue fever since the Aedes aegypti mosquito first appeared in the state more than a decade ago, Patch reported. UC Berkeley postdoctoral scholar Lisa I. Couper, lead author of a June study on dengue risk, told UC Berkeley News in June that "California is on the edge of temperature suitability for dengue." The Aedes aegypti needs only a bottle cap of standing water to breed, according to Orange County Vector Control District spokesperson Brian Bannon.
South Bay residents in Manhattan Beach, Hermosa Beach, Redondo Beach, El Segundo and Hawthorne are served by the LA County West Vector Control District. The district offers free property inspections to help homeowners find and eliminate standing water where mosquitoes breed. Residents can call (310) 915-7370 to request a visit.
LA County Health Officer Dr. Muntu Davis has urged residents to use EPA-registered insect repellent, repair torn screens on windows and doors and dump any standing water around the home weekly.
